Fire alarm system

ABSTRACT

A FIRE ALARM SYSTEM WHICH UTILIZES A PLURALITY OF LOW ENERGY FIRE DETECTION UNITS, EACH OPERATING SOLELY FROM ENERGY RECEIVED FROM A FIRE AND EACH BEING CAPABLE OF PRODUCING AND TRANSMITTING A STABILIZED RADIO FREQUENCY SIGNAL IN RESPONE TO AN ENVIRONMENTAL TEMPERATURE CHANGE RESULTING FROM A FIRE. A SINGLE REMOTE ALARM UNIT RECEIVES AND DEMODULATES THE TRANSMITTED SINGAL RECEIVED FROM ONE OR MORE DETECTION UNITS AND PRODUCES AN AUDIBLE AND/OR VISUAL ALARM IN RESPONSE THERETO. THE SENSITIVITY OF THE DETECTION UNITS IS MADE ADJUSTABLE AND THE RADIO FREQUENCY SIGNAL FROM EACH OF SUCH UNITS MAY BE APPROPRIATELY MODULATED BY AN AUDIO FREQUENCY SIGNAL. THE FREQUENCY VALUES OF SUCH RADIO FREQUENCY SIGNALS AND/OR AUDIO FREQUENCY SIGNALS MAY BE DIFFERENT FOR EACH DETECTION UNIT AND SUCH SIGNALS MAY BE SUITABLY UTILIZED AT THE RECEIVER ALARM UNIT TO IDENTIFY THE LOCATION OF THE FIRE.

mam xaII-wm A. BISBERG FIRE ALARM SYSTEM 5 Sheets-Sheet 1 Filed Sept.13, 1967 ALARM APPARATUS AMPLIFIER DEMODULATOR I I I I I I I l I I 1 I II I I I I I I I I I 74w FREQUENCY STABIL IZING SIGNAL PRODUCING SYSTEMELEMENT f 7 SENSITIVITY TEMPERATURE l2 ADJUSTMENT SENSING ELEMENTFEET-FT FTECETVET? UNTT EFT-E I I I I I I l I I L DETECTOR UNIT FIG. I

FIG. 2

37 AMPLIFIER DEMODULATOR CIRCUIT FIG 3 ARTHUR BIQBERG A 7' TORNFYS"COOCH AND O/CONNELL A. BISBERG FIRE ALARM SYSTEM Filed Sept. 13, 1967 3Sheets-Sheet 2 ROOM RooM n A} 56 5a 50 70 ROOM1 WW POWER f2 56 58 SOURCE10 Rfibfiz w 59 DEMODULATOR I CIRCUIT I f l n 5a 4 IO ALARM APPARATUSFIG. 7

EEES RELAYS f A. AMPLIFIER fb AQ AND RELAY2 v62 DEMODULATOR I CIRCUITRYfn i A RELAYn 62 I POWER 0 SOURCE FIG. 8

- TRANSISTOR FIG 2A l/Vl/E/VTOR' ARTHUR BISHERG ATTORNEYS;

COOCH AND O'CONNELL Jan. 26, 1971 A. BISBERG FIRE ALARM SYSTEM 3Sheets-Sheet 5 Filed Sept. 13, 1967 TUNNEL DIODE ARTHUR Etlahf F16;

FIG. 6

COOCH AND O'CONNELL United States Patent-= 3,559,194 FIRE ALARM SYSTEMArthur Bisberg, Lexington, Mass., assignor, by mesne assignments, toGeneral Eastern Corporation, Boston, Mass., a corporation ofMassachusetts Filed Sept. 13, 1967, Ser. No. 667,577 Int. Cl. G08b 17/12US. Cl. 340-224 Claims ABSTRACT OF THE DISCLOSURE A fire alarm systemwhich utilizes a plurality of low energy fire detection units, eachoperating solely from energy received from a fire and each being capableof producing and transmitting a stabilized radio frequency signal inresponse to an environmental temperature change resulting from a fire. Asingle remote alarm unit receives and demodulates the transmitted signalreceived from one or more detection units and produces an audible and/orvisual alarm in response thereto. The sensitivity of the detection unitsis made adjustable and the radio frequency signal from each of suchunits may be appropriately modulated by an audio frequency signal. Thefrequency values of such radio frequency signals and/or audio frequencysignals may be different for each detection unit and such signals may besuitably utilized .at the receiver alarm unit to identify the locationof the This invention relates generally to systems for detecting thepresence of fire and for providing a warning alarm to the occupants ofabuilding or others and, more particularly, to a system for producing anoscillating signal having a stabilized frequency in the radio-frequencyrange, such signal being generated solely in response to energy obtainedfrom the fire itself, and for transmitting said signal to a remotereceiver alarm unit.

In fire alarm systems, particularly those which are adaptable for use inhomes or-, ,business establishments, it has long been desired to obtaina system which is reliable and relatively inexpensive and which can beeasily installed, tested and maintained by an untrained individual, suchas a homeowner himself. Presently available fire alarm systems usuallyrequire relatively high manufacturing costs and-include elaborate wiringarrangements which in turn increase installation and maintenance costsso as to make the overall expense to the average home owner excessivelyhigh, if not generally prohibitive. Moreover, even relatively expensivepresently known systems are not always reliable, especially thosesystems using wires which are subject to damage or destruction by thefire itself thereby causing the system to fail to operate at the verytime when it is needed.

- Moreover, wireless fire alarm systems which have been proposed up tonow utilize self-contained detection-alarm units having powerrequirements so high that the overall unit does not operate effectivelyor the detection portion thereof requires auxiliary external power, asfrom A-C power lines or batteries, in order to provide a sensing signalwhich has sutficient power to actuate an audible alarm loud enough to beheard in other parts of a building. A-C power failure or limited batteryshelf life contribute to the danger of system failure. Such self-contained wireless units as are now known are not capable of providing aremote alarm indication which is more desirable in most practicalapplications.

The system of this invention, on the other hand, provides an overallcapability for detecting fire at many dilferent locations throughout abuilding or group of buildings and for further providing an alarmindication "ice at an appropriately located remote point such as at ornear the bedroom of a home, for example, to Warn the occupants of thepresence of fire. Moreover, the system can be manufactured so as to sellat a relatively low cost in comparison to presently available systemsand, as will subsequently be shown, is capable of being installed withlittle effort by a homeowner or other untrained individual. Furthermore,the system is extremely reliable and requires little or no maintenancefor continued reliable operation.

-In order to achieve the superior operation of the system of theinvention, the invention utilizesone or more self-energized firedetection units, suitably located throughout a building, and a remotelylocated receiver unit. The fire detection units produce a frequencystabilized oscillating signal as a result of a rate of rise inenvironmental temperature. Such units require little energy foroperation and, since they comprise elements which operate solely inresponse to energy produced by the fire itself, they do not requireexternal sources of power. Moreover, such low energy units are extremelysensitive to small changes in environmental temperatures, thelevel ofsuch sensitivity being capable of adjustment over a relatively widerange to provide an output oscillatiri'g signal in response to a rate oftemperature rise as low "as 15 F. per minute.

...In one preferred embodiment of the invention, for example, such aunit includes means for providing a stabilized radio-frequency carriersignal which is suitably modulated by an audio frequency oscillatingsignal produced in response to the output of a thermoelectrie sensingelement. Such modulated R-F signal is thereupon transmitted to a remotereceiver warning alarm unit. ap-

P propriately placed in the building. The received modulated signal isthen amplified and appropriately demodulated to provide an actuationsignal for an alarm such'as a bell, gong, buzzer, or other suitableindicator which can alert the occupants of the building to the presenceof the fire. Since no external power sources are required for theplurality of fire detection units located at the points where the fireis likely to occur, reliability of the overall system is considerablyincreased over presently known fire alarm systems.

In order to appreciate the advantages of the system of the invention,the operation thereof can be best' described in more detail withreference to the accompanying drawings in which:

FIG. 1 shows a block diagram of the overall system of the invention;

FIG. 2 shows a representative circuit used in the selfcontained firedetection unit of FIG. 1;

FIG. 2a shows an alternate embodiment of a portion of the circuit shownin FIG. 2;

FIG. 3 shows a representative circuit of a remote receiver alar-m unitof the invention;

FIG. 4 shows a pictorial representation of a typical fire detector unitof the invention;

FIG. 5 shows a pictorial representation of a typical remote receiveralarm unit of the invention;

FIG. 6 shows an alternative embodiment of the circuitry which can beused in the fire detection unit of FIG. 1; and

FIG. 7 shows an embodiment of the overall system of the invention foridentifying the location of a fire as well as providing an alarm; and

FIG. 8 shows an alternative embodiment of the overall system of theinvention. 7

As can be seen in the block diagram configuration shown in FIG. 1, thesystem comprises at least one, and preferably more thon one, firedetector unit 10 and a receiver unit 11. Fire detector unit 10 is aself-contained unit which responds to a rate of change in temperature ofthe environment in which it is placed and thereupon produces an outputoscillating signal in the radio fre quency range which can betransmitted by an appropriate antenna 16. Receiver unit 11 receives thetransmitted signal at an appropriate antenna 17 and suitably utilizesthe incoming signal to trigger an alarm apparatus.

The receiver unit may be placed in an appropriate location, such as ator near the bedroom of a house, and one or more fire detector units canbe placed at various other locations, remote from the receiver unit,throughout the house wherever the likelihood of fire may exist. A singlereceiver unit, thus, can be used to provide an alarm in response to manydifferent detector units.

In general, each detector unit is provided with a temperature sensingelement 12 for providing a D-C output voltage in response to a rate ofrise of the environmental temperature and a signal producing circuitresponsive to such voltage for producing a radio frequency oscillatingsignal. The frequency of the latter signal is appropriately stabilizedby a frequency stabilization device 14 and the signal is applied to anantenna 16 for transmission. The sensitivity of the overall unit may beadjusted by a signal adjusting element 15 which is used to set the pointat which oscillation of the signal producing circuit begins in responseto the voltage output from element 12. Receiver unit 11 receives thetransmitted oscillating signal by way of antenna 17 which signal is thenapplied to an appropriate amplifier-demodulator circuit 18 to produce asignal for actuating an appropriate alarm apparatus 19. Theamplifier-demodulator circuit is energized via a suitable power source20 which may be conventional 60-cycle A-C line power or a batterysource. Thus, only the single receiver unit of the overall systemrequires an external power source and reliability of the system isextremely high.

FIG. 2 shows a representative circuit for fire detector unit in which athermoelectric generator 22 produces an output voltage in response to anenvironmental temperature change. The operation of thermoelectricgenerator 22 depends on the well-known Seebeck effect in which a D-Coutput voltage results from a difference in temperature between twodissimilar metals having a common junction. In a suitable thermoelectricgenerator for use in the invention, the dissimilar metals may be abismuth-telluride combination in which a plurality of hot junctions 23are in contact with a suitable'cold junction 24 to produce a D-C voltageat line 21. Cold junction 24 may be appropriately attached to a heatsink, such as the wall of the room, while hot junctions 23 extend intothe interior of the room where they are appropriately exposed to thetemperature therein. D-C output voltage 21 is thereupon applied in theembodiment shown to a tunnel diode element which produces an outputoscillating signal, the frequency of which can be controlled by the useof an output tuned circuit 29 comprising a parallel connected inductance30 and capacitance 31.

In the particular embodiment shown, circuit 29 may be tuned so as toproduce a signal in the audio frequency range which can then be used tomodulate a fixed carrier frequency signal in the radio frequency rangewhich carrier signal is generated by the operation of parallel circuit25 which includes a quartz crystal 28 and a tuned circuit combination ofinductance 26 and capacitance 27. Carrier frequency generator circuit 25produces a signal in the radio frequency range which, when amplitudemodulated by the audio signal from the output of tuned circuit 29, canbe transmitted by antenna'16 to a remote location. The sensitivity ofthe overall unit may be appropriately varied by adjusting the value of avariable resistor 33. The use of a bismuth-telluride thermoelectricgenerator enhances the sensitivity of the unit since it can produce avoltage sufficient to cause oscillatory operation of tunnel diode 32 inresponse to a rate of rise of environmental temperature as low as F. perminute. Variable resistor ,33 allows. such sensitivity to be modulatorcircuit 37, which, for example, may be in the form of a multi-stagetransistor receiver circuit. Such circuit produces an audio outputsignal for operating a relay 39 which, when its contacts are closed,actuates alarm apparatus 40 as shown. Appropriate power is supplied toamplifier-demodulator 37, for example, from an A-C power source 43, suchas the conventional A-C line power source found in the home. The A-Cpower from power source 43 is appropriately converted to D-C voltage bya suitable power supply rectifier 42 and an appropriate panel light 41can be used to indicate that the unit is in operation.

FIG. 4 shows a pictorial representation of one particular embodiment ofa typical fire detector unit 10 of the invention. -In such figure theunit is shown as comprising a mounting section 44 having a rear mountingplate 46 on which thermoelectric generator 22 is mounted with its hotjunctions 23 exposed to the environmental temperatnre via openings 45 inan appropriate cover 38 which in apreferred embodiment is fabricatedfrom a suitable plastic material. Cold junction material 24 is mountedon a rear mounting plate 46 which operates as a heat sink which can bebonded to the wall of a room, for example. Appropriate inductance,resistance and capacitance elements are also mounted on rear mountingplate 46 along with tunnel diode 32. An externally available screwdriveradjustment 60 for varying the position of the movable arm of variableresistor 33, for example, is provided for adjusting the sensitivity ofthe operation of unit 10, that is, for controlling the voltage level atwhich oscillation occurs. An antenna 16 radiates R-F energy via anaperture 47 in side wall 48 of mounting structure 44. The overallstructure is very light in weight and can be bonded to the wall of aroom by screws or by an appropriate adhesive placed on its rear surface.Thus, detector unit 10 can be installed in any desired location by anuntrained individual, such as the homeowner or any member of thehousehold.

A pictorial representation of receiver unit 11 is shown in FIG. 5wherein an appropriate A-C plug 49 is mounted at the rear wall 50 of theoverall alarm unit case. A screwdriver adjustment 51 for varying thegain of the amplifier-demodulator circuit and, hence, the loudness of anaudio alarm, for example, is placed on a side wall thereof. Thus, thereceiver unit can be easily installed by a homeowner merely by pluggingit in at the rear of the unit to a conventional A-C outlet.

Although the circuitry shown in FIG. 2 for fire detector unit 10represents one preferred embodiment thereof, other alternativeembodiments such as the one shown in FIG. 6, for example, may be used.In such figure, thermoelectric generator 22 produces an output voltagewhich can be applied to tunnel diode 32, the output of which is tuned soas to produce an oscillating signal having a frequency in the radiofrequency range by means of a tuned circuit 52 comprising inductance 53,capacitance 54 and a frequency stabilizing quartz crystal 55. Such asystem thereby provides an unmodulated R-F frequency signal at antenna16, the frequency of which is determined by the values of the elementsof tuned circuit 52 and is stabilized specifically by means of quartzcrystal 55. In such an embodiment, the receiver system can merely betuned to the particular radio frequency involved and then appropriatelyamplified and detected to produce an alarm actuation signal.-

As can be seen from the figures, -fire detector unit is made up ofelements which are relatively small and, therefore, its overall size issuch as to provide an extremely lightweight unit occupying little space.Such a unit can be inconspicuously placed in a room where it is noteasily seen or it can be made in a decorative fashion so as not todetract fromthe overall decor of the room. Its size permits easyhandling and, as mentioned above, the unit can be made with anappropriate adhesive backing so as to be easily placed in anyappropriate location and just as easily removed therefrom. An importantadvantage of the system is that it can be readily tested at any time 'bya homeowner. Because of its high sensitivity, the remote alarm unit canbe actuated by arelatively small rate of rise in environmentaltemperature. Hence, a simple non-destructive method of checking theoperation of the system can be readily made merely by placing thefingers on the detection unit or by breathing thereon. Such actioncauses a sufficient temperature rise to produce an appropriate audiblealarm at the remote receiver unit. Such a unit provides a uniqueadvantage over presently known systems which require relatively hightemperatures in order to test the alarm system.

The receiver unit 11 can be easily adapted to provide for an alarm whichis essentially self-locking in that once it is actuated it remainsactuated until turned off. Thus, even if the temperature environmentshould be temporarily reduced for some reason, the alarm remains in anactuated condition to continue to warn the occupants.

Although in order to provide an extremely sensitive system, thepreferred embodiment of fire detector unit 10 is shown as utilizing atunnel diode element responsive to a relatively low excitation voltagesuch element may be replaced, for example, by a transistor oscillatorcircuit, such as shown in FIG. 2a wherein transistor 63' is connected toline 21 and thence to tuned circuit 29. -In either event, appropriatefrequency stabilization can be obtained by utilizing a quartz crystal,or other suitable stabilizing means. Different tuned circuit and crystalcombinations can provide for different carrier frequencies in separatefire detector units. 'In this way the overall system can be madefrequency selective so that, if the remote receiver is arranged toemploy a plurality ofseparate input tuned circuits, it can be used notonly to indicate the presence of a fire, but also to produce anappropriate signal to identify the location of the fire in accordancewith the frequency of the incoming signal. In addition, in thoseembodiments of fire detector unit 10 which utilize an audio frequencymodulation signal, the tunnel diode circuit, for example, can be tunedto produce signals having different audio frequencies for different firedetector units. Thus, by utilizing different radio frequencies as wellas different audio modulation frequencies, a wide variety of selectionand identification means can be obtained.

One such embodiment is shown in FIG. 7 wherein a plurality of firedetection units 10 are placed in a plurality of different roomsdesignated as Room 1, Room 2 Room n as shown. Each of said detectionunits is tuned to produce an output R-F signal tuned to a differentfrequency designated by f f i A receiver unit 11 has an antenna forreceiving said signals and for feeding one or more of them to aplurality of tuned circuits 56, each of said circuits tuned to adifierent frequency corresponding to the frequencies f f f,,. If asignal is present at the output of any one of tuned circuits 56 suchsignal is thereupon fed to an a-mplifier58 and thence to a demodulatorcircuit 59, supplied with power from power source 60, to actuate alarmapparatus 19. The output signals from each of amplifiers 58 areseparately connected to suitable indicators 57, such as appropriatepanel lamps, one or more of which is thereupon actuated by the presenceof a signal at the output of' one or more of said amplifiers to identifythe location of the fire.

Alternatively, the system shown in FIG. 8 may be used wherein aplurality of fire detection units 10 are placed in a plurality ofdifferent rooms in the same manner as suggested above with reference toFIG. 7. In the case of the system shown in FIG. 8, each unit is tuned soas to produce the same R-F reference signal 1",, which is modulated byan appropriate audiosignal f f f as shown, A receiver unit 11 has anantenna for receiving said signals and for feeding them to appropriateamplifier-demodulator circuitry 61 capable of producing one or moreaudio frequency signals corresponding to the audio frequency signalsfrom fire detection units 10. When an audio frequency signal is present,it actuates an appropriate resonant reed delay 62 which thereby producesan audible signal for indicating the presence of fire. The frequency ofthe audible tone can provide an indication of the location of the fireor, alternatively, the relay actuation signal may be appropriately usedto actuate any other suitable display means for identifying the locationof the fire.

Thus, the overall system of the invention can be made extremely flexibledepending on the application for which it is used. A selection of theactual configuration depends primarily on the degreeof complexity whichone is willing to utilize in the receiver unit and the fire detectorcircuit can be made to operate as an amplitude modulation, frequencymodulation or pulse modulation system with suitable changes well knownto those in the art.

Although the various embodiments of the system described in the figuresare shown as utilizing antenna means which may be in the form of asuitable ferrite loop antenna, for example, the system can be made tooperate without an antenna at all if the required range of transmissionis relatively short. Moreover, in some applications the oscillatingsignal may preferably be transmitted to the receiver via absorption of aportion thereof by the power lines of the house.

The receiver unit can be either operated via line power or from abattery source or from both. In the latter case the battery may beappropriately connected to the power line source so as to remain on atrickle charge so that if the line power fails, the battery which isthereby suitably charged, can be automatically switched into the circuitfor operating .the receiver. Concurrently, an auxiliary alarm may beactuated, if desired, to indicate that power failure has occurred. Thus,the chance of a system failure due to faulty receiver operation can bereduced considerably and overall system reliability is furtherincreased.

To further improve the versatility of the system, the receiver unit canalso be made to operate from a voltage produced by presently known smokedetection devices, such as those utilizing photocell systems whichoperate in response to a change in light impinging thereon, such as maybe brought about by the presence of smoke accompanying a fire. Asuitable photoelectric, or other, smoke detector device may be placedadjacent the receiver unit and its output signal can be applied theretoso that the overall system is capable of producing an alarm actuationsignal in response to the presence of smoke as well as to the presenceof fire.

What is claimed is: 1. A fire alarm system comprising: at least one firedetection means including temperature sensing means operating solelyfrom energy received from a fire for producin a voltage in response to arate of change of environmental temperature; I

tunnel diode circuit means for-producing a radio frequency oscillatingsignal in response to said voltage whenever said voltage has a valuecorresponding to a rate of change of environmental temperature ofapproximately 15 F. per minute or greater; 7

a quartz crystal means for'stabilizing the frequency of said oscillatingsignal;

means for transmitting said oscillating signal; and remote meansincluding means for receiving said transmitted oscillating signal;

means for amplifying said received signal to produce an amplified alarmsignal; and

alarm circuit means for producing an alarm in response to said amplifiedsignal.

2. A fire alarm system in accordance with claim 1 wherein said tunneldiode circuit means includes variable adjusting means for controllingthe voltage level at which said oscillating signal is produced.

3. A fire alarm system comprising i a plurality of fire detection units,each of said units comprising temperature sensing means operating solelyfrom energy received from a fire for producing a voltage in response toan environmental temperature change due to said fire;

solid state circuit means for producing an oscillating signal inresponse to said voltage whenever said voltage has a value correspondingto a rate of change of environmental temperature of approximately 15 F.per minute or greater, the frequency of said oscillating signal beingdifferent in each of said fire detection units;

quartz crystal means for stabilizing the frequency of said oscillatingsignal; and

means for transmitting said oscillating signal;

remote receiving means for receiving said transmitted oscillatingsignals; said receiving means including a plurality of filter circuitsfor producing a plurality of separate signals, each of said filtercircuits being responsive to one of said oscillating signals;

means for amplifying each of said separate signals to produce one ormore separate output signals;

a plurality of separate indicator means each responsive to one of saidseparate output signals for producing an indication of the location ofsaid fire; and

means for producing an alarm in response to any one of said separateoutput signals.

4. A fire alarm system in accordance with claim 3 wherein said solidstate circuit means produces an audio frequency oscillating signal, thefrequency thereof being different in each of said fire detection unitsand further includes;

means for producing a radio frequency oscillating signal; means formodulating said radio frequency oscillating signal with said audiofrequency oscillating signal; and said transmitting means transmits saidmodulated signal; and wherein said remote receiving means includes meansfor receiving said modulated signal; means for amplifying anddemodulating said modulated signal; and said alarm producing meansproduces an alarm in response to said demodulated signal. 5. A firealarm system in accordance with claim 4 wherein said temperature sensingmeans comprises a bismuthtelluride element having hot and coldjunctions, said hot junction extending into a temperature changingenvironment and said cold junction thermally connected to a heat sink;and said solid state circuit means comprises a tunnel diode circuit.

References Cited UNITED STATES PATENTS THOMAS B. HABECKER, PrimaryExaminer P. PALAN, Assistant Examiner US. Cl. X.R.

